1. Field Of The Invention
The invention relates to pressure container assemblies and more specifically to such containers having resilient, deformable bladders therein.
2. Prior Art
Pressure control tanks are well known in the prior art and have been used in water supply systems, hot water heating systems or other water systems for many years. Generally, such tanks provide a small quantity of pressurized water to the system upon demand when the pump is off or, when in hydronic systems, allow for expansion of the water within the system to avoid damage to pipes, valves, boiler, etc.
In its most rudimentary form, such an assembly, commonly referred to as a hydro-pneumatic tank, comprises a tank having connections to the system to allow water to flow into and out of the tank. Air entrapped within the tank is compressed by the rising water level to pressurize the system. However, the large size of such tanks has rendered them impractical for modern applications.
It is known to introduce pressurized air into the tank. This also has drawbacks since some of the air is absorbed by the water and passed into the system. The air in the systems may cause corrosion to develop, the heating of a hot water heating system inconsistent, and generate noise or other deleterious characteristics in the system.
The prior art has often resolved this problem to a large extent by installing a flexible diaphragm in the tank to prevent direct contact between the water and the pressurized air. The periphery of the diaphragm is attached to the interior of the tank and it flexes as the quantity of water in the tank increases or decreases. As with any other element in a system containing water, the life span of the accumulator tank is also limited by the effects of corrosion. Water coming into contact with the metal tank causes rust which eventually contaminates the water system and/or causes the tank to leak. Many prior art tanks have minimized or eliminated the corrosion problem by placing a liquid impervious liner within the tank to prevent contact between the metal tank and the water.
Accumulators in general are chambers wherein incompressible liquid may act upon a compressible medium which maintains the liquid under pressure. Air is preferred to springs as the compressible medium since it is lighter. When air is used, it must be carefully isolated from the liquid since it would dissolve into liquid under pressure and come out of solution when the pressure is relieved, creating troublesome air pockets and bubbles. For this reason a flexible partition is provided between air and liquid. This partition may be in the form of a diaphragm or a bladder.
British Pat. No. 909,109 describes a separation bladder for dividing the interior of the pressure vessel into two separate chambers. The bladder is made of resilient deformable material having its greatest internal diameter in the region adjacent and including the mouth. Note the shapes of the non-stressed bladders in FIGS. 1 to 3.
U.S. Pat. No. 3,931,834 describes an expansion tank diaphragm assembly. The tank is divided into non-communicating chambers by a flexible diaphragm having peripherally outward projecting arms and a side wall engaging protrusion that is held in compression and sealing engagement with the tank walls by a backup ring. The diaphragm appears to have uniform diameter and thickness. Note the shape of unstressed diaphragm 32 and line 22.
West German Offenlegungsschrift No. 2,754,606 describes a diaphragm which divides the interior of a hydropneumatic pressure accumulator into an upper and lower half chambers. The edge of the diaphragm is secured against the inside of the lower housing of the accumulator by means of a holder member. The inner surface of the lower half corresponds to the shape of the diaphragm in the unstretched condition, while that of the upper half is larger than the surface of the unstretched diaphragm when inverted about the holder member.
European Patent Application No. 218,304 describes a bladder type diaphragm fitted in an expansion tank. The shaped diaphragm is held in position by at least one annular open holding element.
U.S. Pat. No. 2,378,517 describes accumulators having a one-piece shell and a bladder for separating a compressible fluid from a relatively incompressible liquid.
See also U.S. Pat. Nos. 3,722,751, 3,887,104, 4,264,108 and 4,697,674 and British Pat. No. 2,111,939.